This invention relates in general to sewing machines and, in particular, to the feeding mechanisms of the type shown in the U.S. Pat. No. 693,852 to Free and particularly adapted for commercial heavy-duty sewing machines.
In the sewing of heavy fabrics such as, for example, automobile upholstering, or heavy brocades, as in furniture upholstering, or in any industry where large amounts of heavy fabrics are utilized, the feed dog which is responsible for the movement of the fabric in a forward or reverse direction across the work bed of a sewing machine for the sewing operation, takes up a heavy work load which is then imposed on the feed bar and the link mechanism which cntrols the length and direction of the stitch of the machine. Often the working conditions are such that the fabric being pushed and pulled sometimes falls off the machine, thus imposing extremely large forces on the feed dog pulling the fabric across the work bed, which large forces are ultimately absorbed by the feed mechanisms within the machine with large moments imposed by the linkages on the bearings and shafts therein. Prior art machines, a typical example of which is the heavy duty type machine as shown in the Engel U.S. Pat. No. 3,012,531, compensated for such loads by utilizing heavy bearings located in heavy webs in the machine frame. Thus, as shown in the patent, the shaft 30 is housed in rather large bearings 32, journalled in the web of the machine frame with the toggle links 42 and 43 and bridge 33 imposing large moments of force on these bearings when the machine is sewing heavy fabric.
Also, in order to compensate for the forces imposed by the work load on the sewing machine, it has heretofore been necessary to provide a web in the machine frame strong enough to support a large bore to receive a large bearing so as to absorb the work forces thereon, especially when such forces are magnified by the lever action involved in the toggle and bridge, such as shown in the Engel patent, supra.
This invention, however, provides large bearing surfaces on the lever and links themselves by utilizing a supporting ring for a complementary ring-shaped feed stroke adjusting element which is anchored or fastened to the web of the machine bed by simple machine screws so that thick webs and large bores for large bearings and bearing loads have been eliminated. With this double ring arrangement, all of the levers and toggles necessary to function as a drag link feeding mechanism can be made compact, thus reducing the bearing forces and moments of force while at the same time providing a larger bearing surface for these forces.